A fixing device with a heating roller and a pressure roller is known as one used in image forming apparatuses such as laser beam printers or copying machines. This type of fixing device nips a sheet of recording medium bearing an unfixed toner image on it between the heating roller and the pressure roller, while it transports the recording medium, to apply heat and pressure to fix the toner image onto the recording medium.
Multiple heater lamps are placed as heat sources in the heating roller. In general, as the printing rate or the ream weight of paper supported by the image forming apparatus goes higher, the heat capacity required to fix the toner image increases. To maintain the temperature of the heating roller at or above a certain level, the fixing temperature goes higher and higher.
When the heating roller having been maintained at a high temperature comes to the end of its service life, it has to be replaced with a new one. In this case, operations of the image forming apparatus are stopped to cool down the heating roller to a temperature suitable for the replacement work. Then, a maintenance technician removes the heating roller from the fixing device and replaces it with a new heating roller. Such replacement and maintenance work include time for cooling down the heating roller, and the work efficiency becomes low. In addition, since the down time of the image forming apparatus increases, the operational efficiency of the image forming apparatus is degraded and the cost burden for the replacement and maintenance work increases.
In recent years and continuing, it is required for image forming apparatuses to have abilities of high-speed printing, high-quality image reproduction and compatibility with various types of recording media. The fixing device is also required to deal with such demands and several types of heating rollers are used depending on the purposes. For example, a PFA coated heating roller (coated with a thin film of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin) is used aiming at promptly supplying heat required for fixing toner images. To achieve a high-image quality, a heating roller coated with silicon rubber is used to prevent the toner image from darkening and blurring during the fixing process. When durability is emphasized, while achieving a certain degree of image quality, a heating roller coated with a PFA tube over the silicon rubber layer is used.
FIG. 1 is a cross-sectional view of a conventional fixing device and FIG. 2 is a perspective view of replacement of a heating roller disclosed in, for example, WO 91/09351.
As illustrated in FIG. 1, one end of the heating roller 100 is supported via a bearing flange 101 at a frame 102. The bearing flange 101 has a bearing 103 which is fit, together with a centering member 104, into the opening of the heating roller 100. Although not shown in the figure, the other end of the heating roller 100 is also supported at a bearing flange via a bearing.
The bearing flange 101 is fixed to the frame 102 by means of a wing screw 106. A retaining claw 108 is fixed to the bearing flange 101 by means of a wing screw 107. The retaining claw 108 functions to fix the heating roller 100 when replacing the heating roller 100 with a new one.
A lamp cartridge with multiple heater lamps is placed in the heating roller 100. One end of the lamp cartridge is held at the center of the bearing flange 101 via the retaining member 109. Although not shown in the figure, the other end of the lamp cartridge 105 is also held indirectly at the bearing flange 101 via a retaining member.
A connector 110 provided at the end of the lamp cartridge 105 holds the lamp cartridge 105 at the center of the bearing flange 101, and projects from the bearing flange 101 outward. The bearing flange 101 is furnished with a grip 111 for replacement of the heating roller 100 as a single unit. The grip 111 is positioned over the connector 110 of the lamp cartridge 105 projecting from the bearing flange 101.
When replacing the heating roller 100, prior to the replacement, the connector 110 projecting from the bearing flange 101 of the lamp cartridge 105 is gripped and pulled out along the axis of the heating roller 100. Then, as illustrated in FIG. 2, the wing screw 106 is loosened, and the heating roller 100 is pulled out from the frame 102, together with the bearing flange 101, while the grip 111 is gripped by a hand. To prevent the heating roller 100 from touching the frame 102 when passing through the opening of the frame 102, felt is applied to the periphery of the opening of the frame 102 so as not to scratch the heating roller 100.
The lamp cartridge 105 with multiple heater lamps has to be removed prior to the replacement of the heating roller 100. Since the lamp cartridge 105 is longer than the heating roller 100 and easily broken, it has to be treated carefully during the removal and the insertion.
The heating roller 100 used in this type of fixing device has a cylindrical shape with a diameter of 100 mm and a length of 500 mm, and is considerably heavy by itself.
Under such circumstances, a maintenance technician grips by one hand the grip 111, while supporting the heating roller 100 by the other hand wearing a glove 120, to pull out the heating roller 100, together with the bearing flange 101, from the frame 102 for the replacement of the heating roller 100. During the replacement, the motion may become unstable due to the weight and the heat of the heating roller 100. Accordingly, the heating roller 100 is likely to come in contact with the other parts, such as the frame 102, during the replacement, and be damaged or subjected to scratches on the surface of the roller.
The position of the heating roller 100 is unstable during the replacement. Besides the heating roller 100 is held by a gloved hand without using an aiding device in the prior art method. The maintenance technician may suffer burns if touching the high-temperature heating roller 100, and the glove 120 gets dirty due to the mold lubricant or the grease adhering on the heating roller 100. Thus, the operability is degraded.
In addition, when the maintenance technician pulls out the heating roller 100 together with the bearing flange 10 from the frame 102 by holding the grip 111 by one hand, the opening of the frame 102 and the inside of the retaining member 130 are covered with felt so as to protect the roller surface from being damaged due to undesirable contact with the frame 102. However, since the heating roller 100 contaminated by the mold lubricant or the grease slides over the felt, the felt is stained by grease builtup and insufficient for protecting the surface of the heating roller 100.
Felt has to be attached and removed every time the heating roller 100 is replaced, which makes the replacement work troublesome. Since felt is stained every time the heating roller 100 is replaced, disposal of the old felt and arrangement of new felt are required.
A structure for preventing breakage when pulling out the lamp cartridge 105 is proposed by JP 2002-23535 A. FIG. 3 is a cross-sectional view of a heating roller from which a lamp cartridge 127 is to be pulled out.
When pulling out the lamp cartridge 127 from a heating roller 114, an operator is positioned behind the image forming apparatus (on the side of a second lamp holder 129 shown in FIG. 3) to insert a lamp-protection cylinder member 164 through a hole 159a formed in a housing 159. The inner periphery of the end of the cylinder member 164 is fit into a protector holding unit 130 provided to the first lamp holder 128, whereby the cylinder member 164 is held to protect the lamp.
When the cylinder member 164 has been set, the operator moves to the front of the image forming apparatus (on the side of the first lamp holder 128 in FIG. 3) to take off the restriction member 165 from a recess (not shown) to release the restriction on the movement of the lamp cartridge 127 in the axial direction. In this state, the lamp cartridge 127 is pulled out together with the cylinder member 164 from the heating roller 114.
This method can prevent breakage of the lamp cartridge 127 during the insertion and the pullout, and handling ability is improved. However, the lamp cartridge 127 has to be removed prior to replacement of the heating roller 114, and the work efficiency is not satisfactory.
Thus, the fixing device disclosed in WO 91/09351 has defects in that the lamp cartridge has to be removed and refixed before and after the replacement of the heating roller. This work increases the number of steps of the replacement process and makes the replacement work cumbersome.
The method disclosed in JP 2002-23535 A can improve the safety in the insertion and pullout of the lamp cartridge; however, complication of the work sequence has not been solved yet.